Control apparatus for vehicle

ABSTRACT

An engine control device, while executing a fuel-cut control, calculates a target intake air amount (Qat) from a basic intake air amount (Qabase) and an added intake air amount (Qaadd) commensurate with an accessory torque (step S 14 ). Next, the engine control device acquires a coolant temperature (Tw) (step S 15 ), and then sets a lower-limit intake air amount (Qamin) (step S 16 ). When the target intake air amount (Qat) is smaller than the lower-limit intake air amount (Qamin) (NO in step S 17 ), the engine control device updates the target intake air amount (Qat) with the lower-limit intake air amount (Qamin). (step S 18 ), and adjusts the degree of throttle opening so that the actual intake air amount (Qa) becomes equal to the target intake air amount (Qat) (step S 19 ).

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2009-282821 filed onDec. 14, 2009, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control apparatus for a vehicle which iscapable of stopping the supply of fuel to an internal combustion engineduring deceleration.

2. Description of the Related Art

Generally, a vehicle equipped with an internal combustion engine isdesigned to perform a fuel-cut process of stopping the supply of fuel tothe internal combustion engine so as to improve fuel economy.

Such a vehicle is designed so that after an accelerator pedal of thevehicle is released and the vehicle begins to decelerate, the fuel-cutcontrol of stopping the supply of fuel to the internal combustion engineis executed until the engine rotation speed of the internal combustionengine drops to a predetermined value. Then, after the engine rotationspeed drops to the predetermined value, the vehicle ends the executionof the fuel-cut and starts supplying fuel again in order to preventoccurrence of engine stall.

Among vehicle control apparatuses that execute the fuel-cut control,there is known a control apparatus that switches between the executionand the non-execution of the fuel-cut according to the temperature of acatalyst that is disposed in an exhaust passageway of the internalcombustion engine, so as to prevent degradation of the catalyst (see,e.g., Japanese Patent Application Publication No. 11-62664(JP-A-11-62664)).

The vehicle control apparatus described in Japanese Patent ApplicationPublication No 11-62664 (JP-A-11-62664) is designed to execute thefuel-cut control when the degree of throttle opening is a fully closeddegree and the rotation speed of the internal combustion engine isgreater than or equal to a predetermined value.

It is to be noted herein that if a fuel-lean exhaust gas passes throughthe catalyst in a high temperature state, the excess supply of oxygenaccelerates the growth of particles of platinum (Pt) in the catalyst.Therefore, the total surface area of Pt that contacts exhaust gas in thecatalyst reduces, so that the exhaust gas control performance declines.

Therefore, the vehicle control apparatus described in Japanese PatentApplication Publication No. 11-62664 (JP-A-11-62664) determines whetheror not the catalyst is in a high temperature state during execution ofthe fuel-cut control. When it is determined that the catalyst is in thehigh temperature state, the control apparatus prohibits execution of thefuel-cut control even if the condition for executing the fuel-cutcontrol is satisfied. In this manner, the control apparatus prevents thecatalyst from being exposed to lean exhaust gas and therefore preventsreduction of the surface area of Pt in the catalyst, and thus maintainsthe exhaust emission control performance.

On another hand, if the fuel-cut control is prohibited during the hightemperature state of the catalyst as described above while the internalcombustion engine is warming up, misfire may occur due to unstablecombustion resulting from high viscosity of the lubricating oil of theengine or low atomization of fuel. If unburnt fuel is supplied togetherwith exhaust gas into the catalyst, and ignites therein, the catalystperformance is rather likely to degrade. Therefore, the vehicle controlapparatus described in Japanese Patent Application Publication No.11-62664 (JP-A-11-62664) discontinues the prohibition of the fuel-cutcontrol during the warming-up of the internal combustion engine, even ifthe catalyst is in the high temperature state.

Beside, generally in conjunction with the vehicle control apparatusesthat execute the fuel-cut control as described above, since combustionis unstable during the warming-up state of the internal combustionengine (during a state in which the engine is being warmed up), thelikelihood of occurrence of engine stall heightens if the fuel-cutcontrol is ended while the engine rotation speed has become low.Therefore, during the warming-up state, the engine rotation speed atwhich to end the fuel-cut control is set higher than after the end ofthe warming-up, so as to prevent occurrence of engine stall.

Therefore, when the engine is being warmed up, the continuation time ofthe fuel-cut becomes shorter and therefore improvement of the fueleconomy is hampered, in comparison with when the engine has been warmedup. Therefore, in order to realize improved fuel economy, it isadvisable to delay the end of the fuel-cut control as much as possibleby adopting a construction in which the engine rotation speed at whichto end the fuel-cut control during the warming-up of the engine is setlower than in the related art.

However, the related-art vehicle control apparatus described in JapanesePatent Application Publication No. 11-62664 (JP-A-11-62664) is notdesigned so that the engine rotation speed at which to end the fuel-cutcontrol during the warming-up of the engine is set lower than in therelated art. Therefore, if the fuel-cut control during the warming-up ofthe engine is executed at lower engine rotation speeds than in therelated art, it is likely that when the supply of fuel is started again,the combustion will be unstable and the engine rotation speed will notrise, and therefore a drawback, such as engine stall or the like, willoccur.

SUMMARY OF THE INVENTION

In view of the foregoing problems of the related art, the inventionprovides a control apparatus for a vehicle which is capable of improvingfuel economy without causing engine stall in conjunction with theexecution of the fuel-cut control during the warming-up of the engine,and capable of preventing deterioration of driveability at the end ofthe fuel-cut control.

To that end, according to one aspect of the invention, there is provideda vehicle control apparatus which is installed in a vehicle thatincludes an intake gas flow adjustment mechanism that is disposed on anintake passageway of an internal combustion engine and that adjusts anintake air amount that is taken into the internal combustion engine, andwhich adjusts the intake air amount by controlling the intake gas flowadjustment mechanism, and which includes: a coolant temperature detectorthat detects coolant temperature of the internal combustion engine; afuel supply stop device that stops supply of fuel to the internalcombustion engine on a condition that the engine rotation speed of theinternal combustion engine is greater than or equal to a predeterminedvalue during deceleration of the vehicle; an intake air amount-settingdevice that sets the intake air amount based on a running condition ofthe vehicle; a control device that controls the intake gas flowadjustment mechanism so as to realize the intake air amount that is setby the intake air amount-setting device; and a lower limit value-settingdevice that sets a lower limit value of the intake air amount accordingto the coolant temperature detected by the coolant temperature detector,wherein the lower limit value-setting device sets the lower limit valueof the intake air amount higher when the coolant temperature detected bythe coolant temperature detector is relatively low than when the coolanttemperature is relatively high, and the control device controls theintake gas flow adjustment mechanism so that the intake air amount takeninto the internal combustion engine becomes equal to the lower limitvalue, when the intake air amount set by the intake air amount-settingdevice is less than the lower limit value set by the lower limitvalue-setting device while the supply of fuel has been stopped by thefuel supply stop device.

According to another aspect of the invention, there is provided acontrol method which is for a vehicle that includes an intake gas flowadjustment mechanism that is disposed on an intake passageway of aninternal combustion engine and that adjusts an intake air amount that istaken into the internal combustion engine, and which adjusts the intakeair amount by controlling the intake gas flow adjustment mechanism.

-   detecting coolant temperature of the internal combustion engine;-   stopping supply of fuel to the internal combustion engine on a    condition that engine rotation speed of the internal combustion    engine is greater than or equal to a predetermined value during    deceleration of the vehicle;-   setting the intake air amount based on a running condition of the    vehicle; and-   controlling, the intake gas flow adjustment mechanism so as to    realize the intake air amount set,-   wherein a lower limit value of the intake air amount is set    according to the coolant temperature detected, and the lower limit    value of the intake air amount is set higher when the coolant    temperature is relatively low than when the coolant temperature is    relatively high, and the intake gas flow adjustment mechanism is    controlled so that the intake air amount taken into the internal    combustion engine becomes equal to the lower limit value, when the    intake air amount is less than the set lower limit value while the    supply of fuel has been stopped.

According to the foregoing vehicle control apparatus and the vehiclecontrol method, the intake air amount taken into the internal combustionengine can be increased when the supply of fuel is stopped during thewarming-up of the engine, during which the coolant temperature is low.Therefore, during the warming-up of the engine, during which there ishigh possibility of misfire being caused by relatively low atomizationof fuel or relatively high viscosity of lubricating oil, fuel can becertainly burned when the supply of fuel is started again. Therefore,although the engine rotation speed at which to end the fuel-cut controlduring the warming-up of the engine is set lower than in the relatedart, the engine rotation speed can be certainly made high at the end ofthe fuel-cut control. Hence, it is possible to re-start the supply offuel later than in the related art without causing engine stall. As aresult, fuel economy can be improved.

In the vehicle control apparatus, the lower limit value-setting devicemay set another lower limit value for causing absolute value of negativepressure in a combustion chamber of the internal combustion engine to beless than or equal to a predetermined value when the supply of fuel hasbeen stopped by the fuel supply stop device, and may set the anotherlower limit value as a new lower limit value when the coolanttemperature is in a range of the coolant temperature in which theanother lower limit value is higher than the lower limit value that isset according to the coolant temperature.

Besides, in the foregoing vehicle control method, another lower limitvalue for causing absolute value of negative pressure in a combustionchamber of the internal combustion engine to be less than or equal to apredetermined value when the supply of fuel has been stopped may be set,and the another lower limit value may be set as a new lower limit valuewhen the coolant temperature is in a range of the coolant temperature inwhich the another lower limit value is higher than the lower limit valuethat is set according to the coolant temperature.

According to the foregoing vehicle control apparatus and the foregoingcontrol method, it is possible not only to prevent engine stall duringthe warming-up of the engine but also to prevent the oil that lubricatesthe internal combustion engine from entering the combustion chamber andbeing consumed therein due to the negative pressure of the internalcombustion engine.

Besides, in the foregoing vehicle control apparatus, the intake gas flowadjustment mechanism may be constructed of a throttle valve, and thecontrol device may control degree of opening of the throttle valve.

According to the foregoing vehicle control apparatus, the intake airamount can be adjusted without complicating the construction of theintake gas flow adjustment mechanism. Besides, even though the lowerlimit value of the intake air amount is set high, sufficient intake airamount can be secured by increasing the degree of throttle opening.

Besides, in the foregoing vehicle control apparatus, the intake gas flowadjustment mechanism may have a throttle valve, and an idle speedcontrol valve that i actuated during an idling state of the internalcombustion engine, and the control device may control degree of openingof the throttle valve and degree of opening of the idle speed controlvalve.

According to the foregoing vehicle control apparatus, even though thelower limit value of the intake air amount is set high, sufficientintake air amount can be secured by increasing the degree of throttleopening.

According to the invention, it is possible to provide a controlapparatus for a vehicle which is able to improve fuel economy bypreventing engine stall when executing the fuel-cut control during thewarming-up of the engine, and is able to prevent deterioration ofdriveability at the end of the fuel-cut control.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, advantages, and technical and industrial significance ofthis invention will be described in the following detailed descriptionof example embodiments of the invention with reference to theaccompanying drawings, in which like numerals denote like elements, andwherein;

FIG. 1 is a general construction diagram showing a construction of anengine and its surroundings in accordance with an embodiment of theinvention;

FIG. 2 is a general construction diagram showing a control apparatus fora vehicle in accordance with an embodiment of the invention;

FIG. 3 is a diagram showing an intake air amount lower-limit-value mapin accordance with an embodiment of the invention; and

FIG. 4 is a flowchart showing an intake air amount control in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a control apparatus for a vehicle 1 in accordance with anembodiment of the invention will be described with reference to FIGS. 1to 4. Firstly, a construction will be described.

As shown in FIG. 1, an engine 2 that is an internal combustion enginemounted in the vehicle 1 is a four-stroke cycle gasoline engine thatundergoes a series of four strokes, that is, the intake stroke, thecompression stroke, the expansion stroke and the exhaust stroke, duringtwo back-and-force movements of a piston 2 (described later).Incidentally, although this embodiment is described on the assumptionthat the engine 2 is an in-line four-cylinder gasoline engine, theengine according to the invention is not limited so, but may also be anyof other various kinds of engines, for example, an in-line six-cylinderengine, a V-type six-cylinder engine, a V-type twelve-cylinder engine, aflat six-cylinder engine, etc.

The engine 2 has an engine body section 3, a fuel supply section 4, anintake section 5, and an exhaust section 6. The following descriptionwill be made mainly in conjunction with one of the four cylinders 22arranged in line, as an example.

The engine body section 3 has: a cylinder block 13 that is fixed to avehicle body via an engine mount (not shown); a cylinder head 15 fixedto a side of the cylinder block 13; a head cover 18 fixed to thecylinder head 15; a crank case 19 fixed to another side of the cylinderblock 13; and an oil pan 20 that is fixed to the crank case 19 and thatis constructed so as to be capable of storing lubricating oil.

A water jacket 14 in which a coolant is caused to flow is formed in thecylinder block 13, so that the water jacket 14 cools the cylinder block13 through heat exchange with the coolant.

Intake ports 16 and exhaust ports 17 are formed in the cylinder head 15.Besides, the cylinder block 13 and the cylinder head 15 define acylinder (actually, four cylinders) 22.

Besides, the engine body section 3 has a cylindrical piston 23 that ishoused in the cylinder block 13 so as to be slidable in an axisdirection of the cylinder 22. The cylinder block 13, the cylinder head15 and the piston 23 together define a pent roof type combustion chamber24.

A plurality of piston ring grooves are formed in a side peripheralsurface portion of the piston 23. Piston rings that contact an innerperipheral surface of the cylinder block 13 are fitted into theindividual piston ring grooves. Since the piston 23 slides with thepiston rings in contact with the inner peripheral surface of thecylinder block 13, the piston 23 slides within the cylinder 22 in theaxis direction thereof while the combustion chamber 24 is keptsubstantially air-tight.

Besides, the engine body section 3 has a crankshaft 26 that is housed inthe crankcase 19 and that constitutes an output shaft of the engine 2,and a connecting rod 27 that links the piston 23 and the crankshaft 26.The engine body section 3 is constructed so that reciprocating motion ofthe piston 23 is converted into rotary motion of the crankshaft 26 viathe connecting rod 27.

The crankshaft 26 has: crank journals that are rotatably supported bythe crankcase 19; a plurality of crank arms that are protruded radiallyfrom the crank journals; crank pins formed between predetermined ones ofthe crank arms so as to be parallel to the crank journals withpredetermined interaxial distances; and counter weights that areprovided at radially opposite sides to the crank pins and that areformed integrally with crank arms, respectively.

The connecting rod 27 has a rod body that is formed in a bar shape. Therod body has a small end portion in which a small bearing hole isformed, and, at the opposite side of the rod body to the small endportion, a large end portion in which a large bearing hole is formed.The small end portion is constructed so that a piston pin attached tothe piston 23 is rotatably inserted into the small bearing hole andtherefore the small end portion links the piston 23 and the connectingrod 27 via the piston pin. The large end portion of the connecting rod27 is constructed so as to link the connecting rod 27 and the crankshaft26 with the crank pin inserted into the large bearing hole.

Furthermore, the engine body section 3 has a valve-operating mechanism28 that is fixed to the cylinder head 15, an ignition device 35 that isfixed to the head cover 18, and an injector 37 that is disposed near thecylinder head 15.

The valve-operating mechanism 28 is constructed of a variable valvemechanism (e.g., VVT-i, or Variable Valve Timing-intelligent system)that optimally controls the open/close timing of each of intake valves29 and exhaust valves 30 according to the running condition of thevehicle 1. Besides, the valve-operating mechanism 28 has the intakevalves 29 and the exhaust valves 30 of a rocker arm type, and an intakecamshaft 32 and an exhaust camshaft 33 that are rotatably supported. Thevalve-operating mechanism 28 converts rotation of the intake camshaft 32and the exhaust camshaft 33 into reciprocating motion of the intakevalves 29 and the exhaust valves 30 via the rocker arms. Therefore, thevalve-operating mechanism 28 switches the state of communication of theintake ports 16 and the exhaust ports 17 with the combustion chamber 24at optimum open/close timing according to the running condition of thevehicle 1, by moving the intake valves 29 and the exhaust valves 30 backand forth.

The intake camshaft 32 and the exhaust camshaft 33 are each supportedrotatably by a camshaft housing (not shown) that is fixed to thecylinder head 15, and are constructed so as to rotate in interlock withthe crankshaft 26 via a timing chain (not shown). Besides, the intakecamshaft 32 and the exhaust camshaft 33 have cams that contact rockerarms that each correspond to one of the intake valves 29 and the exhaustvalves 30, and therefore push down each rocker arm at everypredetermined rotation angle of a corresponding one of the cams.

The piston 23, the crankshaft 26, the connecting rod 27 and thevalve-operating mechanism 28, which are described above, are constructedso as to be lubricated and cooled by oil that is pumped from the oil pan20 and is circulated by a torochoid type oil pump.

The ignition device 35 has a spark plug 36 which is formed of a centerelectrode and a ground electrode and a portion of which is protrudedinto the combustion chamber 24. The electric current supplied to anignition coil of the ignition device 35 is controlled by an enginecontrol device 80 so that the ignition device 35 ignites a mixture offuel and air at optimum timing.

The injector 37 is constructed of a port ignition type fuel injectiondevice, and has a fuel injection portion in which a small fuel injectionhole is formed and a portion of which is exposed to an interior of theintake port 16, and a drive portion that switches the open/closed stateof the fuel injection hole by using an electromagnetic valve that iscontrolled by the engine control device 80. The injector 37 is suppliedwith fuel that is pressurized to a predetermined pressure by a fuel pump42 described below. Besides, when the electromagnetic valve iselectrified, the injector 37 opens its fuel injection hole and injectsthe pressurized fuel in an atomized state into the intake port 16. Onthe other hand, when the electromagnetic valve de-electrified, theinjector 37 closes the fuel injection hole and therefore refrains frominjecting fuel.

the injector 37 is not limited to the port ignition type, but may alsobe constructed by an in-cylinder injection type fuel injection devicethat injects fuel directly into the combustion chamber 24, and may alsoemploy a combination of a port ignition type fuel injection device andan in-cylinder injection fuel injection device.

The fuel supply section 4 has an iron or resin-made fuel tank 41 whoseinterior has been treated with a rust prevention process, and acircumferential flow-type fuel pump 42 that is housed in the fuel tank41. The fuel supply section 4 is designed so as to supply fuel that hasbeen pressurized to a predetermined pressure by the fuel pump 42, to theinjector 37 via a fuel delivery pipe. Incidentally, in the case wherethe foregoing in-cylinder injection type fuel injection device is used,the fuel supply section 4 may further has a high-pressure fuel pump thatsupplies high-pressure fuel to the in-cylinder injection type fuelinjection device, as well as the fuel pump 42.

The intake section 5 has: an intake pipe 51 that is connected at a sideend thereof to the cylinder head 15; an air filter 52 connected to asecond end side of the intake pipe 51; a single-valve type throttlevalve 55 provided in the intake path between the cylinder head 15 andthe air filter 52; and a throttle actuator 56 that is constructed of anelectronically controlled motor that is controlled by the engine controldevice 80. The intake section 5 is constructed so as to introduce airinto the engine body section 3. Incidentally, the intake pipe 51 inaccordance with this embodiment constitutes an example of an intakepassageway in accordance with the invention.

The air filter 52 has a filter case 53 that is connected to the secondend side of the intake pipe 51, and a filter element 54 that is housedin the filter case 53 and that is made of a non-woven fabric. The airfilter 52 is designed so as to remove dust and the like from the airthat is introduced into the intake section 5 from outside the vehicle.

The throttle valve 55 has a disc shaped valve body, and a valve shaftthat is fixed to the valve body. The throttle valve 55 is designed sothat the valve body is pivoted by pivoting the valve shaft via thethrottle actuator 56, whereby the channel cross-sectional area of air inthe intake pipe 51 is changed. Due to this, the throttle valve 55adjusts the amount of flow of air that is introduced into the enginebody section 3.

Incidentally, the throttle valve 55 in accordance with this embodimentconstitutes an example of an intake gas flow adjustment mechanism inaccordance with the invention.

The exhaust section 6 has an exhaust pipe 61 that is connected at an endside thereof to the cylinder head 15, and a catalytic converter 62. Theexhaust section 6 is constructed so as to discharge exhaust gas producedin the engine body portion 3, to the outside of the vehicle.

The catalytic converter 62 has a converter case 63 that is connected tothe exhaust pipe 61, and a catalyst 64 that is housed in the convertercase 63. The catalyst 64 is constructed of a three-way catalyst in whichan alumina support is loaded with an oxidation-reduction catalyst, suchas platinum, rhodium, palladium, etc. The catalyst 64 substantiallypurifies the exhaust gas produced by combustion of air-fuel mixture byefficiently removing harmful substances, such as unburnt hydrocarbon(HC), carbon monoxide (CO), nitrogen oxides (NOx), etc., which arecontained in exhaust gas.

The catalyst temperature sensor 71 is disposed near the catalyticconverter 62, and detects the temperature of the catalyst 64, andoutputs the temperature to the engine control device 80.

The vehicle 1 further includes the engine control device 80 thatconstitutes a control apparatus for a vehicle in accordance with theinvention. The engine control device 80 is constructed of a known ECU(Electronic Control Unit), and controls the magnitude of torque outputfrom the engine 2, and also executes other various controls describedbelow.

Incidentally, the engine control device 80 in accordance with theembodiment constitutes an example of a coolant temperature detector, afuel supply stop device, an intake air amount-setting device, a controldevice, and a lower limit value-setting device in accordance with theinvention.

A coolant temperature sensor 75 shown in FIG. 2 is constructed of, forexample, a thermistor whose electric resistance changes according totemperature. Therefore, the coolant temperature sensor 75 is designed sothat the resistance of the thermistor changes according to the coolanttemperature Tw of the engine 2, and so that therefore voltage thatchanges according to the coolant temperature Tw is output as a signalthat represents the coolant temperature Tw to the engine control device80. The engine control device 80 detects the coolant temperature Tw onthe basis of the magnitude of the voltage obtained from the coolanttemperature sensor 75. Therefore, the coolant temperature sensor 75 andthe engine control device 80 constitute an example of a coolanttemperature detector in accordance with the invention. The coolanttemperature sensor 75 is attached to an external wall surface of thecylinder block 13 so as to detect the temperature of the coolant thatflows in the water jacket 14.

As shown in FIG. 2, the engine control device 80 is constructed of amicrocomputer that includes a CPU (Central Processing Unit) 81, a RAM(Random Access Memory) 82, a ROM (Read-Only Memory) 83, an EEPROM(Electrically Erasable and Programmable Read-Only Memory, registeredtrademark) 82, an input port 85, an output port 86, etc., which areinterconnected by a bidirectional bus 87. The CPU 81 executes an outputcontrol of the engine 2 and the like by performing the signal processingin accordance with programs and maps stored beforehand in the ROM 83 anddata stored in the EEPROM 84, while utilizing the temporary storagefunction of the RAM 82. The signals output from the output port 86 aresent to the throttle actuator 56 and the like via an A/D converter.

Besides, the engine control device 80 controls the degree of opening ofthe throttle valve 55, the amount of fuel injection and the timing offuel injection of the injector 37, the ignition timing of the spark plug36, on the basis of the signals input from various sensors.

The vehicle 1 further includes an accelerator operation amount sensor72, a vehicle speed sensor 74, an engine rotation speed sensor 76, anoperation position sensor 77 for detecting the operation position of ashift lever 78, a throttle opening degree sensor 79, and the like.

The accelerator operation amount sensor 72 is constructed of, forexample, an electronic position sensor that uses a Hall element. Whenthe accelerator pedal is operated by a driver, the accelerator operationamount sensor 72 outputs to the engine control device 80 a signal thatrepresents an accelerator operation amount Ace that shows the positionof the accelerator pedal. The engine control device 80 controls thedegree of opening of the throttle valve 55 (see FIG. 1), the fuelinjection timing of the injector 37, and the ignition timing of thespark plug 36 (see FIG. 1), so as to cause the engine 2 to generate atorque commensurate with the accelerator operation amount Acc.

The vehicle speed sensor 74 outputs to the engine control device 80 asignal that represents rotation speed Nout of the output shaft. On thebasis of this signal, the engine control device 80 calculates vehiclespeed V.

The engine rotation speed sensor 76, constituting a device that detectsthe engine rotation speed of the engine 2, detects the engine rotationspeed Ne of the engine 2 on the basis of the rotation of the crankshaft26.

The operation position sensor 77 detects the position of the shift lever78, and sends a signal that represents a result of detection to theengine control device 80. On the basis of the signal input from theoperation position sensor 77, the engine control device 80 determinesthe position of the shift lever 78. Besides, the vehicle 1 includes atransmission control device that controls the transmission ratio of theautomatic transmission according to the vehicle speed V and theaccelerator operation amount Acc. The engine control device 80 acquiresa signal that represents the present transmission ratio from thetransmission control device that is connected to the engine controldevice 80 via an in-vehicle LAN line.

The throttle opening degree, sensor 79 is constructed of, for example, aHall element that provides an output voltage commensurate with thedegree of throttle opening of the throttle valve 55 (see FIG. 1). Thethrottle opening degree sensor 79 outputs to the engine control device80 a signal that represents the degree of throttle opening of thethrottle valve 55.

A characteristic construction of the engine control device 80 inaccordance with the embodiment of the invention will be described withreference to FIG. 1 to FIG. 3. When the vehicle 1 is decelerating, theengine control device 80 executes a fuel-cut control. Concretely, theengine control device 80 starts the fuel-cut control provided that thesignal input from the accelerator operation amount sensor 72 is a signalthat represents the closed state of the accelerator operation amount,and that the signal that is input from the engine rotation speed sensor76 and that represents the engine rotation speed Ne is within apredetermined range in which the fuel-cut can be executed, and that thepresent transmission ratio input from the transmission control device isa transmission ratio that allows execution of the fuel-cut.

Thus, the engine control device 80 in accordance with this embodimentconstitutes an example of a fuel supply stop device in accordance withthe invention.

On the basis of the signal input from the engine rotation speed sensor76, the engine control device 80 ends the fuel-cut control when theengine rotation speed Ne of the engine 2 becomes lower than apredetermined value. Incidentally, with regard to the engine controldevice 80 in accordance with this embodiment, the engine rotation speedNe at which to end the fuel-cut control is set lower than the enginerotation speed Ne at which to end the fuel-cut control in the relatedart because of execution of an intake air amount control that isdescribed in detail below, so that the fuel-cut control ends later thanin the related art. Besides, the engine rotation speed Ne at which toend the fuel-cut control is determined beforehand at a value at whichengine stall does not occur, through empirical measurement.

In the case where the vehicle 1 is equipped with a torque converter thatincludes a lockup mechanism, the lockup mechanism is set into an engagedstate or a slipping engagement state along with execution of thefuel-cut control, so as to delay the decline of the engine rotationspeed Ne of the engine 2. In this case, the transmission control deviceswitches the lockup mechanism between the engaged state and the slippingstate according to the present transmission ratio.

Besides, the engine control device 80 calculates a basic intake airamount Qabase that represents a basic value of the amount of intake airthat is taken into the combustion chamber 24 during the fuel-cutcontrol. Concretely, the engine control device 80, after acquiring fromthe engine rotation speed sensor 76 a signal that represents the enginerotation speed Ne, calculates the basic intake air amount Qabase withreference to a basic intake air amount map in which the engine rotationspeed Ne and the basic intake air amount Qabase are associated with eachother in correspondence. The basic intake air amount map is defined sothat the greater the engine rotation speed Ne, the greater the basicintake air amount Qabase.

Besides, the engine control device 80 calculates an added intake airamount Qaadd that is needed according to an accessory torque.Concretely, the ROM 83 of the engine control device 80 pre-stores anairconditioner torque map in which the duty ratio of a compressor of anairconditioner and the rotation speed are associated in correspondencewith the torque of an airconditioner pulley. After acquiring the dutyratio of the compressor and the rotation speed of the airconditionerpulley, the engine control device 80 calculates a torque that is neededin order to drive the airconditioner with reference to theairconditioner torque map.

Besides, the engine control device 80 calculates an accessory torquethat is needed in order to drive a coolant pump. The coolant pump isprovided at an inlet opening side of a coolant circuit that includes thewater jacket 14 and that is formed in the cylinder block 13. The enginecontrol device 80 pre-stores in the ROM 83 the torque that is generatedaccording to the state of driving of the coolant pump as a coolant pumptorque map. With reference to the coolant pump torque map, the enginecontrol device 80 calculates the torque that is needed in order to drivethe coolant pump.

Besides, the engine control device 80 pre-stores in the ROM 83 thetorque that is generated according to the driving state of thealternator. With reference to the alternator torque map, the enginecontrol device 80 calculates the torque that is needed in order to drivethe alternator.

The engine control device 80 pre-stores in the ROM 83 the added intakeair amount map in which the accessory torque and the added intake airamount Qaadd are associated in correspondence. After totaling theaccessory torques that are needed in order to drive the foregoingaccessories, the engine control device 80 acquires an added intake airamount Qaadd with reference to the added intake air amount map stored inthe ROM 83.

Besides, the engine control device 80 calculates a target intake airamount Qat by summing the basic intake air amount Qabase and the addedintake air amount Qaadd. Therefore, the engine control device 80 inaccordance with this embodiment constitutes an example of an intake airamount-setting device that sets an intake air amount on the basis of therunning condition of the vehicle 1.

Besides, the engine control device 80 sets a lower-limit intake airamount Qamin on the basis of an intake air amount lower-limit-value mapthat will be described below.

The intake air amount lower-limit-value map in accordance with thisembodiment is expressed by a graph in which the coolant temperature Twand the intake air amount Qa are associated in correspondence as shownin FIG. 3.

During the warming-up of the engine 2, that is, during a state in whichthe coolant temperature Tw is low, the lubricating oil that lubricatesthe piston 23 and the like in the cylinder block 13 has low temperature.Therefore, the viscosity of the oil is higher during the warming-up thanafter the warming-up ends, so that the friction force that occurs whenthe piston 23 slides increases. During the warming-up of the engine, theatomization of fuel injected from the injector 37 into the intake port16 deteriorates and, in the case of the fuel injection from the portignition type injector, there occurs a port-wet phenomenon in which aportion of the fuel injected deposits on a wall surface of the intakeport 16, so that combustion becomes unstable.

Therefore, the related-art engine control device is designed so thatduring the warming-up of the engine, the engine rotation speed Ne atwhich to end the fuel-cut control is set higher than after the end ofthe warming-up in order to give higher priority to the prevention ofengine stall resulting from misfire than to improvement of fuel economywhen the supply of fuel into the combustion chamber is re-started at theend of the fuel-cut control.

On the other hand, in the engine control device 80 in accordance withthis embodiment, the engine rotation speed Ne at which to end thefuel-cut control is set lower than in the related art in order toimprove fuel economy, and despite of this setting, the occurrence ofengine stall due to misfire is prevented by performing the intake airamount control with reference to the intake air amount lower-limit-valuemap, even when the supply of fuel into the combustion chamber 24 isre-started at the end of the fuel-cut control.

That is, while the engine 2 is being warmed up, the engine controldevice 80 in accordance with this embodiment makes the intake air amountQa larger during execution of the fuel-cut control than during normaloperation, in order to prevent occurrence of engine stall due tomisfire.

Due to this, generally, there occurs a response delay from when thedegree of opening of the throttle valve 55 is adjusted to when theintake air amount supplied to the combustion chamber 24 changes.However, in this embodiment, as an optimal amount of intake air is takenin beforehand during the fuel-cut control, the intake air amount Qa isan optimum value even when the fuel-cut control ends and fuel issupplied into the combustion chamber 24 again. Therefore, occurrence ofengine stall can be prevented.

The combustion in the combustion chamber 24 becomes more unstable thelower the temperature of the engine is, that is, the lower the coolanttemperature Tw is. Therefore, in the intake air amount lower-limit-valuemap, the lower limit value of the intake air amount Qa determined so asto prevent occurrence of engine stall is set higher, the lower thecoolant temperature Tw, as shown by a solid line 91 in FIG. 3.

Besides, if while the vehicle 1 is traveling, the accelerator operationamount Acc enters a closed state and, during deceleration, the throttlevalve 55 is closed, great negative pressure occurs within the intakepipe 51 at the downstream side of the throttle valve 55 and within theintake port 16 (hereinafter, referred to as intake pipe interior). Ifgreat negative pressure occurs within the intake pipe interior, theeffect thereof changes the in-cylinder pressure in the combustionchamber 24 into negative pressure, so that so-called oil lift occurs.The oil lift becomes a cause of the consumption of oil in the combustionchamber 24. Therefore, from the viewpoint of restraining the oilconsumption, it is desirable to avoid occurrence of excessive negativepressure within the intake pipe 51 at the downstream side of thethrottle valve 55 and within the intake port 16.

The degree of closeness of the relationship between this oil lift andthe coolant temperature is lower than the degree of closeness of therelationship between the occurrence of engine stall and the coolanttemperature. Therefore, in the intake air amount lower-limit-value mapin accordance with this embodiment, a constant value Qanp of intake airamount for restraining the oil lift is set regardless of the coolanttemperature Tw, as shown by an interrupted line 92.

Besides, as indicated by an arrow-shaped scale 93 in FIG. 3, the greaterthe intake air amount Qa during the fuel-cut control, the greater thetorque step between before and after the fuel-cut control ends becomes,and the more deteriorated the driveability of the vehicle 1 becomes.Therefore, qualitatively, the intake air amount Qa is preferred to be assmall as possible, as long as engine stall does not occur. In thisembodiment, the lower limit value of the intake air amount Qa that isrepresented by the solid line 91 and the interrupted line 92 is set sothat driveability will not deteriorate. Besides, the lower limit valueof the intake air amount decreases as the coolant temperature Tw becomeshigher and therefore the possibility of occurrence of engine stalldecreases. Therefore, driveability can be further improved. That is, ina range where the intake air amount Qa is above the interrupted line 92,the solid line 91 is defined so as to achieve the prevention ofoccurrence of engine stall and improvement of driveability in goodbalance.

In the embodiment, the engine control device 80 determines whether ornot the target intake air amount Qat calculated as described above is ina settable range 94 that is defined by the lower limit values that arerepresented by the solid line 91 and the interrupted line 92. If thetarget intake air amount Qat is not in the settable range 94, the enginecontrol device 80 executes a guard process of replacing the calculatedtarget intake air amount Qat with one of the lower limit valuesrepresented by the solid line 91 and the interrupted line 92 whichcorresponds to the coolant temperature Tw detected by the coolanttemperature sensor 75.

That is, the engine control device 80 is constructed so as to set thelower limit value of the intake air amount higher when the detectedcoolant temperature is relatively low than when the detected coolanttemperature is relatively high.

Besides, the interrupted line 92 in accordance with this embodimentconstitutes another lower limit value of the intake air amount inaccordance with the invention. That is, the engine control device 80 inaccordance with this embodiment has a construction in which anotherlower limit value of the intake air amount for causing the absolutevalue of the negative pressure in the combustion chamber of the internalcombustion engine to be less than or equal to a predetermined value whenthe supply of fuel is stopped is set, and the another lower limit is setas a new lower limit value of the intake air amount when the coolanttemperature is in a range of coolant temperature in which the anotherlower limit value is higher than the lower limit value that is setaccording to the coolant temperature. Therefore, the engine controldevice 80 in accordance with this embodiment constitutes an example of alower limit value-setting device in accordance with the invention.

Besides, the engine control device 80 adjusts the degree of opening ofthe throttle valve 55 by controlling the throttle actuator 56 so thatthe actual intake air amount Qa becomes equal to the target intake airamount Qat. Concretely, the engine control device 80 stores in the ROM athrottle opening degree map in which the target intake air amount Qatand the degree of throttle opening are associated with each other incorrespondence. When a target intake air amount Qat has been set, theengine control device 80 acquires a degree of throttle opening withreference to the throttle opening degree map. Then, the engine controldevice 80 controls the throttle actuator so as to achieve the degree ofthrottle opening. Therefore, the engine control device 80 in accordancewith this embodiment constitutes an example of a control apparatus inaccordance with the invention.

Besides, in the case where the vehicle 1 is equipped with an intake airamount sensor, the engine control device 80 may execute a feedbackcontrol so that the intake air amount detected by the intake air amountsensor, that is, the actual intake air amount, becomes closer to thetarget intake air amount Qat.

Next, operations will be described with reference to FIG. 4.Incidentally, the process described below is realized by a program thatis pre-stored in the ROM 83, and is executed by the CPU 81 atpredetermined time intervals.

As shown in FIG. 4, firstly, the engine control device 80 determineswhether or not the fuel-cut control is being executed (step S11). Theengine control device 80 executes the fuel-cut control in the case wherethe fully closed state of the accelerator operation amount Acc isdetected by the accelerator operation amount sensor 72 and where theengine rotation speed Ne is greater than or equal to a predeterminedvalue. During execution of the fuel-cut control, the engine controldevice 80 sets up in the EEPROM 84 a flag that shows execution of thefuel-cut control, and determines whether or not the fuel-cut control isbeing executed on the basis of this flag.

If it is determined that the fuel-cut control is being executed (YES instep S11), the engine control device 80 proceeds to step S12. On theother hand, if it is determined that the fuel-cut is not being executed(NO in step S11), the engine control device 80 proceeds to a RETURNstep.

If the answer to the determination in step S11 is YES, the processproceeds to step 12, in which the engine control device 80 calculates abasic intake air amount Qabase. Concretely, the engine control device 80acquires from the engine rotation, speed sensor 76 a signal thatrepresents the engine rotation speed Ne, and calculates a basic intakeair amount Qabase from the engine rotation speed Ne with reference tothe basic intake air amount map stored in the ROM 83.

Next, the engine control device 80 calculates an added intake air amountQaadd commensurate with the accessory torque (step S13). Concretely, theengine control device 80 acquires signals that represent the states ofdriving of the airconditioner compressor, the coolant pump and thealternator, and then calculates an accessory torque therefrom on thebasis of the airconditioner torque map, the coolant pump torque map andthe alternator torque map. Then, with reference to the added intake airamount map, the engine control device 80 calculates an added intake airamount Qaadd that corresponds to the accessory torque.

Next, the engine control device 80 calculates a target intake air amountQat from the basic intake air amount Qabase calculated in step S12, andthe added intake air amount Qaadd commensurate with the accessory torquewhich is calculated in step S13, by using the following expression (1):Qat=Qabase+k×Qaadd  (1)where k is a coefficient that is determined beforehand by empiricalmeasurement.

Next, the engine control device 80 acquires the coolant temperature Tw(step S15). Concretely, the engine control device 80 acquires thecoolant temperature Tw on the basis of the signal input from the coolanttemperature sensor 75.

Next, the engine control device 80 sets a lower-limit intake air amountQamin (step S16). Concretely, with reference to the intake air amountlower-limit-value map stored in the ROM 83, the engine control device 80sets a lower limit value of the intake air amount which corresponds tothe coolant temperature TW acquired in step S15, as a lower-limit intakeair amount Qamin.

Next, the engine control device 80 determines whether or not the targetintake air amount Qat is greater than or equal to the lower-limit intakeair amount Qamin (step S17). If it is determined that the target intakeair amount Qat is greater than or equal to the lower-limit intake airamount Qamin (YES in step S17), the engine control device 80 proceeds tostep S19. On the other hand, if it is determined that the target intakeair amount Qat is less than the lower-limit intake air amount Qamin (NOin step S17), the engine control device 80 proceeds to step S18.

In step S18, the engine control device 80 executes the guard processwith respect to the target intake air amount Qat.Qat←Qamin  (2)

Next, in order to cause the actual intake air amount Qa to become equalto the target intake air amount Qat, the engine control device 80 sets adegree of throttle opening with reference to the foregoing throttleopening degree map, and controls the throttle actuator 56 so as toachieve the set degree of throttle opening (step S19).

As described above, in the vehicle 1 that stops supplying fuel to theengine when the vehicle 1 is decelerating, the engine control device 80in accordance with the embodiment is able to increase the intake airamount Qa supplied into the combustion chamber 24 when the supply offuel is stopped during the warming-up of the engine. Because of this,the engine control device 80 is able to certainly achieve combustion offuel when the supply of fuel is started again during the warming-up ofthe engine, during which there is high possibility of misfire beingcaused by relatively low atomization of fuel or relatively highviscosity of lubricating oil. Therefore, although the engine rotationspeed at which to end the fuel-cut control during the warming-up of theengine is set lower than in the related art, the engine rotation speedcan be certainly made high at the end of the fuel-cut control. Hence, itis possible to re-start the supply of fuel later than in the related artwithout causing engine stall. As a result, fuel economy can be improved.Besides, after the warming-up of the engine ends, the lower limit valueof the intake air amount is set lower than during the warming-up, sothat the torque step that occurs at the time of re-start of the supplyof fuel can be reduced and deterioration of driveability can beprevented.

Besides, the engine control device 80 is able to not only prevent enginestall during the warming-up of the engine but also prevent the oil thatlubricates the pistons 23 and the like from entering the combustionchambers and being consumed therein due to the negative pressure of theinternal combustion engine.

The foregoing description has been made in conjunction with the casewhere the engine control device 80 causes the actual intake air amountQa to approach the target intake air amount Qat during execution of theintake air amount control, by controlling the degree of opening of thethrottle valve 55.

However, it is also possible to adopt a construction in which the intakesection 5 of the vehicle 1 is equipped with an ISC (Idle Speed Control)bypass passageway for adjusting the amount of flow of air supplied tothe engine 2 when the operation state of the engine 2 is an idlingstate, and in which the engine control device 80 performs bothadjustment of the degree of opening of the throttle valve 55 andadjustment of the amount of flow of air through the ISC bypasspassageway. In this case, the ISC bypass passageway is provided with anISC valve for adjusting the amount of air flow, and the ISC valve isdriven so as to change the amount of air flow in the ISC bypasspassageway by an ISC valve actuator that is controlled by the enginecontrol device 80. In this case, for example, the degree of opening ofthe ISC valve is adjusted when the coolant temperature Tw is high, andthe degree of opening of the throttle valve 55 is adjusted when thecoolant temperature Tw is low so that the target intake air amount Qatcannot be achieved solely by the amount of air flow through the ISCbypass passageway.

Incidentally, since the ISC bypass passageway is generally provided forcontrolling the engine rotation speed Ne during the idling of theengine, the ISC bypass passageway is not sufficient to convey the amountof intake air that is needed in order to maintain combustion immediatelyafter the end of the fuel-cut control during a state in which the engineis being warmed up and the engine rotation speed is low as mentionedabove in conjunction with the embodiment. However, if the ISC bypasspassageway is able to convey the amount of intake air needed in order tomaintain the combustion immediately following the end of the fuel-cutcontrol during the warming-up of the engine at low engine rotationspeed, the engine control device 80 may adjust the degree of opening ofthe ISC valve instead of adjusting the degree of opening of the throttlevalve 55.

Besides, the foregoing description has been made in conjunction with thecase where the solid line 91 in the intake air amount lower-limit-valuemap in FIG. 3 is defined so that the lower limit value of the intake airamount continuously increases with decrease of the coolant temperatureTw. However, the solid line 91 may also be defined so as to provide thesetting of two lower-limit values in which the smaller one of thelower-limit values is selected when the coolant temperature Tw is higherthan or equal to a predetermined value, and the larger lower-limit valueis selected when the coolant temperature Tw is lower than thepredetermined value. In this case, the predetermined value is determinedbeforehand by empirical measurement, on the basis of the state ofatomization of fuel and the viscosity of lubricating oil relative to thecoolant temperature Tw. Besides, the solid line 91 may also bedetermined so as to define not only two lower limit values but alsothree or more lower limit values that are selected in the ascendingorder with decrease of the coolant temperature Tw.

Besides, although the foregoing description has been made in conjunctionwith the construction in which the vehicle 1 is equipped with theautomatic transmission, the invention is not limited to thisconstruction, but the vehicle 1 may have a manual transmission or acontinuously variable transmission. Besides, the vehicle 1 may also be ahybrid vehicle that is driven by an engine and an electric motor. Inthis case, the condition for starting the fuel-cut control changes, incomparison with the case where the vehicle 1 is equipped with anautomatic transmission. However, it is still possible to preventoccurrence of engine stall and improve fuel economy although the enginerotation speed at which to end the fuel-cut control is lower in theengine control device of this embodiment than in the related-art enginecontrol device.

Besides, although according to the foregoing description, the intake airamount lower-limit-value map is defined by the solid line 91 and theinterrupted line 92, the invention is not limited to this construction.For example, the intake air amount lower-limit-value map may be definedby only the solid line 91. In this case, although there is possibilityof increase in the oil consumption due to the oil lift in comparisonwith the case where the intake air amount lower-limit-value map isdefined by the solid line 91 and the interrupted line 92, it is possibleto improve fuel economy as in the foregoing embodiment.

As described above, the control apparatus for a vehicle of the inventionachieves effects of being able to improve fuel economy without causingengine stall in conjunction with execution of the fuel-cut during thewarming-up of the engine, and of being able to prevent deterioration ofdriveability at the end of the fuel-cut control, and is useful to acontrol apparatus for a vehicle that is able to stop the supply of fuelto an internal combustion engine during deceleration.

The invention claimed is:
 1. A vehicle control apparatus which isinstalled in a vehicle that includes an intake gas flow adjustmentmechanism that is disposed on an intake passageway of an internalcombustion engine and that adjusts an intake air amount that is takeninto the internal combustion engine, and which adjusts the intake airamount by controlling the intake gas flow adjustment mechanism,comprising: a coolant temperature detector that detects coolanttemperature of the internal combustion engine; a fuel supply stop devicethat stops supply of fuel to the internal combustion engine on acondition that the engine rotation speed of the internal combustionengine is greater than or equal to a predetermined value duringdeceleration of the vehicle; an intake air amount-setting device thatsets the intake air amount based on a running condition of the vehicle;a control device that controls the intake gas flow adjustment mechanismso as to realize the intake air amount that is set by the intake airamount-setting device; and a lower limit value-setting device that setsa lower limit value of the intake air amount according to the coolanttemperature detected by the coolant temperature detector, wherein thelower limit value-setting device sets the lower limit value of theintake air amount higher when the coolant temperature detected by thecoolant temperature detector is relatively low than when the coolanttemperature is relatively high, and the control device controls theintake gas flow adjustment mechanism so that the intake air amount takeninto the internal combustion engine becomes equal to the lower limitvalue, when the intake air amount set by the intake air amount-settingdevice is less than the lower limit value set by the lower limitvalue-setting device while the supply of fuel has been stopped by thefuel supply stop device.
 2. The vehicle control apparatus according toclaim 1, wherein the lower limit value-setting device sets another lowerlimit value for causing absolute value of negative pressure in acombustion chamber of the internal combustion engine to be less than orequal to a predetermined value when the supply of fuel has been stoppedby the fuel supply stop device, and sets the another lower limit valueas a new lower limit value when the coolant temperature is in a range ofthe coolant temperature in which the another lower limit value is higherthan the lower limit value that is set according to the coolanttemperature.
 3. The vehicle control apparatus according to claim 1,wherein the intake gas flow adjustment mechanism is constructed of athrottle valve, and the control device controls degree of opening of thethrottle valve.
 4. The vehicle control apparatus according to claim 1,wherein the intake gas flow adjustment mechanism has a throttle valve,and an idle speed control valve that is actuated during an idling stateof the internal combustion engine, and the control device controlsdegree of opening of the throttle valve and degree of opening of theidle speed control valve.
 5. The vehicle control apparatus according toclaim 2, wherein the intake gas flow adjustment mechanism is constructedof a throttle valve, and the control device controls degree of openingof the throttle valve.
 6. The vehicle control apparatus according toclaim 2, wherein the intake gas flow adjustment mechanism has a throttlevalve, and an idle speed control valve that is actuated during an idlingstate of the internal combustion engine, and the control device controlsdegree of opening of the throttle valve and degree of opening of theidle speed control valve.
 7. A control method which is for a vehiclethat includes an intake gas flow adjustment mechanism that is disposedon an intake passageway of an internal combustion engine and thatadjusts an intake air amount that is taken into the internal combustionengine, and which adjusts the intake air amount by controlling theintake gas flow adjustment mechanism, comprising: detecting coolanttemperature of the internal combustion engine; stopping supply of fuelto the internal combustion engine on a condition that engine rotationspeed of the internal combustion engine is greater than or equal to apredetermined value during deceleration of the vehicle; setting theintake air amount based on a running condition of the vehicle; andcontrolling the intake gas flow adjustment mechanism so as to realizethe intake air amount set, wherein a lower limit value of the intake airamount is set according to the coolant temperature detected, and thelower limit value of the intake air amount is set higher when thecoolant temperature is relatively low than when the coolant temperatureis relatively high, and the intake gas flow adjustment mechanism iscontrolled so that the intake air amount taken into the internalcombustion engine becomes equal to the lower limit value, when theintake air amount is less than the set lower limit value while thesupply of fuel has been stopped.
 8. The control method according toclaim 7, wherein another lower limit value for causing absolute value ofnegative pressure in a combustion chamber of the internal combustionengine to be less than or equal to a predetermined value when the supplyof fuel has been stopped is set, and the another lower limit value isset as a new lower limit value when the coolant temperature is in arange of the coolant temperature in which the another lower limit valueis higher than the lower limit value that is set according to thecoolant temperature.